Fault diagnosis of electric machines

Abstract

Faults and fault types in electric machines can be identified based on spectra associated with stator and field currents. Signals associated with such currents can be compensated for line variations, and spectral contributions for non-eccentric machines can be reduced or eliminated to permit distinguish static eccentricities from non-eccentric machine operation. One or more of a static eccentricity, a dynamic eccentricity, and a mixed eccentricity can be identified based on spectral component magnitudes at selected frequencies.

We claim: 
     
       1. A method of detecting faults in an operating multi-phase electric machine, comprising:
 measuring a stator current, a field current, or both a stator current and a field current with the operating multi-phase electric machine under load; 
 determining a spectral magnitude at a selected fault frequency based on at least one the stator current and a field current, wherein the selected fault frequency is given by 
 
       
         
           
             
               
                 
                   f 
                   fault 
                 
                 = 
                 
                   
                     ( 
                     
                       
                         n 
                         ± 
                         
                           6 
                           ⁢ 
                           h 
                         
                       
                       ± 
                       
                         km 
                         p 
                       
                     
                     ) 
                   
                   ⁢ 
                   f 
                 
               
               , 
             
           
         
       
       wherein n=1, 5, 7, 11, 13 . . . for stator currents, and 0 for field current, m is a non-negative even integer for static eccentricity, m is 0 for dynamic eccentricity, m is a positive integer for mixed eccentricity, p is a fundamental pole pair number, f is a stator line frequency, and k and h are non-negative integers; and
 indicating an air gap eccentricity fault, a stator inter-turn fault, or both in the multi-phase electric machine based on the determined spectral magnitude and the selected fault frequency. 
 
     
     
       2. The method of  claim 1 , further comprising applying a residue correction to the spectral magnitude, wherein the indicated fault is determined based on the residue-corrected spectral magnitude. 
     
     
       3. The method of  claim 2 , wherein the residue correction is based on spectral characteristics corresponding to a non-eccentric multi-phase machine. 
     
     
       4. The method of  claim 1 , wherein the spectral magnitude is associated with a frequency associated with a dynamic eccentricity, and the residue correction is based on a spectral magnitude corresponding to an air gap lacking static eccentricity. 
     
     
       5. The method of  claim 1 , wherein the indicated fault is associated with an air gap eccentricity. 
     
     
       6. The method of  claim 5 , wherein the indicated fault is associated with a dynamic air gap eccentricity. 
     
     
       7. The method of  claim 5 , wherein the indicated fault is a static air gap eccentricity. 
     
     
       8. The method of  claim 5 , wherein the indicated fault is a mixed static and dynamic air gap eccentricity. 
     
     
       9. The method of  claim 1 , wherein the indicated fault is associated with an inter-turn short circuit. 
     
     
       10. The method of  claim 1 , further comprising selecting a fault frequency based on fault to be identified. 
     
     
       11. The method of  claim 10 , further comprising selecting fault frequencies associated with at least one of a static eccentricity, a dynamic eccentricity, and a mixed eccentricity. 
     
     
       12. The method of  claim 1 , wherein at least the field current is measured, and the spectral magnitude at the selected fault frequency is based on at least one field current. 
     
     
       13. A method of detecting faults in an operating multi-phase electric machine, comprising:
 measuring a stator current, a field current, or both a stator current and a field current with the operating multi-phase electric machine under load; 
 determining a spectral magnitude at a selected fault frequency based on at least one of a the stator current and a field current; and 
 indicating an air gap eccentricity fault, a stator inter-turn fault, or both in the multi-phase electric machine based on the determined spectral magnitude and the selected fault frequency, wherein the selected fault frequency is given by 
 
       
         
           
             
               
                 
                   f 
                   fault 
                 
                 = 
                 
                   
                     ( 
                     
                       
                         n 
                         ± 
                         
                           6 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           h 
                         
                       
                       ± 
                       
                         
                           k 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           m 
                         
                         p 
                       
                     
                     ) 
                   
                   ⁢ 
                   f 
                 
               
               , 
             
           
         
       
       wherein n=1, 5, 7, 11, 13 . . . for stator currents, and 0 for field current, m is a non-negative even integer for static eccentricity, m is 0 for dynamic eccentricity, m is a positive integer for mixed eccentricity, p is a fundamental pole pair number, f is a stator line frequency, and k and h are non-negative integers. 
     
     
       14. At least one computer-readable storage device comprising computer executable instructions stored on a non-transitory computer-readable medium for the method of  claim 13 . 
     
     
       15. An apparatus, comprising:
 interface electronic sensors operable to receive at least one of a stator current signal or a field current signal from an induction machine; and 
 a signal processor configured to calculate a spectral magnitude associated with at least one of a stator current or a field current of the operating induction machine under load at at least one predetermined frequency, and based on the estimated spectral magnitude, indicate at least one of a static eccentricity, a dynamic eccentricity, and a mixed eccentricity, wherein the predetermined frequency is given by at least one of 
 
       
         
           
             
               
                 
                   f 
                   fault 
                 
                 = 
                 
                   
                     ( 
                     
                       
                         n 
                         ± 
                         
                           6 
                           ⁢ 
                           h 
                         
                       
                       ± 
                       
                         km 
                         p 
                       
                     
                     ) 
                   
                   ⁢ 
                   f 
                 
               
               , 
             
           
         
       
       wherein n=1, 5, 7, 11, 13 . . . for stator currents, and 0 for field current, m is a non-negative even integer for static eccentricity, m is 0 for dynamic eccentricity, m is a positive integer for mixed eccentricity, p is a fundamental pole pair number, f is a stator line frequency, and k and h are non-negative integers. 
     
     
       16. The apparatus of  claim 15 , wherein the signal processor is configured to identify at least one of a static eccentricity, a dynamic eccentricity, and a mixed eccentricity based on the spectral magnitude and frequency. 
     
     
       17. The apparatus of  claim 16 , wherein the signal processor is configured to obtain a Fourier transform of the electrical signal and estimate the spectral magnitude based on the Fourier transform. 
     
     
       18. The apparatus of  claim 16 , wherein the signal processor is configured to estimate a contribution of an eccentric condition to the spectral magnitude based on a contribution associated with a non-eccentric condition. 
     
     
       19. The apparatus of  claim 15 , wherein the signal processor is configured to estimate spectral magnitudes at fault frequencies associated with static eccentricity, a dynamic eccentricity, and a mixed eccentricity. 
     
     
       20. The apparatus of  claim 15 , further comprising a signal conditioner configured to couple an electrical signal associated with at least one of the stator current and the field current to the signal processor. 
     
     
       21. The apparatus of  claim 20 , where the signal conditioner is configured to couple the electrical signal associated with at least one of the stator current and the field current to the signal processor as a digitized electrical signal. 
     
     
       22. The apparatus of  claim 15 , wherein the signal processor is configured to estimate the spectral magnitude associated with at least one of the stator current and the field current based on a stator voltage. 
     
     
       23. A method, comprising:
 with a signal processor, obtaining a spectral magnitude associated with at least one of a stator current and a field current in an operating motor under load; and 
 with the signal processor, based on the spectral magnitude and at least one fault frequency, identifying an eccentricity type in a motor, wherein the at least one fault frequency is given be 
 
       
         
           
             
               
                 
                   f 
                   fault 
                 
                 = 
                 
                   
                     ( 
                     
                       
                         n 
                         ± 
                         
                           6 
                           ⁢ 
                           h 
                         
                       
                       ± 
                       
                         km 
                         p 
                       
                     
                     ) 
                   
                   ⁢ 
                   f 
                 
               
               , 
             
           
         
       
       wherein n=1, 5, 7, 11, 13 . . . , for stator currents, and 0 for field current, m is a non-negative even integer for static eccentricity, m is 0 for dynamic eccentricity, m is a positive integer for mixed eccentricity, p is a fundamental pole pair number, f is a stator line frequency, k and h are non-negative integers. 
     
     
       24. An apparatus, comprising:
 interface electronic sensors operable to receive at least one of a stator current signal or a field current signal from an electric machine; and 
 a signal processor configured to estimate a spectral magnitude associated with at least one of a stator current and a field current of an operating induction machine under load, and based on the estimated spectral magnitude, identify at least one of a static eccentricity, a dynamic eccentricity, and a mixed eccentricity, wherein the signal processor is configured to estimate spectral magnitudes at fault frequencies associated with static eccentricity, a dynamic eccentricity, and a mixed eccentricity, wherein the fault frequencies include at least one of 
 
       
         
           
             
               
                 
                   f 
                   fault 
                 
                 = 
                 
                   
                     ( 
                     
                       
                         n 
                         ± 
                         
                           6 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           h 
                         
                       
                       ± 
                       
                         
                           k 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           m 
                         
                         p 
                       
                     
                     ) 
                   
                   ⁢ 
                   f 
                 
               
               , 
             
           
         
       
       wherein n=1, 5, 7, 11, 13 . . . , for stator currents, and 0 for field current, m is a non-negative even integer for static eccentricity, m is 0 for dynamic eccentricity, m is a positive integer for mixed eccentricity, p is a fundamental pole pair number, f is a stator line frequency, and k and h are non-negative integers.